Recently, with increasing demand for improving fuel efficiency of vehicles and with stringent regulations on emissions from vehicles made in many countries, the demand for environmentally friendly vehicles has increased. In order to meet this demand and regulations, the environmentally friendly vehicles, for example, hybrid vehicles and electric vehicles have been developed.
However, these vehicles need to have a power train and a control system that are different from those of a general internal combustion engine vehicle. Therefore, there is the demand for methods of increasing fuel efficiency and reducing exhaust gas, which may also be applied to general vehicles.
As one of these methods, when a deceleration situation is expected ahead, it may be desirable to induce a vehicle to perform driving using inertia (or “coasting”) by prompting a driver to release his/her foot from an accelerator pedal at an appropriate time point, which may prevent unnecessary fuel consumption. In particular, in the case of a hybrid vehicle having an electric driving motor, a reduction in fuel consumption may be anticipated when an accelerator pedal is not operated and a greater increase in fuel efficiency may be anticipated when a hydraulic brake is not used, but only the regenerative braking force of the electric motor is used, when deceleration is required.
In particular, deceleration via such coasting may be more useful when an upcoming deceleration situation (e.g. speed cameras, tollgates, and curved roads) can be more accurately predicted thanks to recently introduced high-precision maps and vehicle sensors. This will be described below with reference to FIG. 1.
FIG. 1 is a view for explaining the concept of general coasting guidance.
Referring to FIG. 1, when a vehicle acquires information regarding an upcoming deceleration event via high-precision maps and vehicle sensors, the remaining distance to the upcoming deceleration event and a target speed of the vehicle may be calculated. When matching the calculated information with coasting distance profiles for each vehicle and for each speed acquired via tests and the like, the distance required for coasting to reach the target speed at the current vehicle speed may be calculated. Thus, when the vehicle gives a driver a notice in a predetermined form at the time point at which the remaining distance to the upcoming deceleration event reaches the required coasting distance, the driver may begin coasting by releasing his/her foot from an accelerator pedal.
Thus, unnecessary fuel consumption is reduced by the amount of time between the time point at which the driver first releases his/her foot from the accelerator pedal and the time point at which the driver performs braking via a brake after visually recognizing the upcoming deceleration event. Of course, no notice may be output when the driver releases his/her foot from the accelerator pedal before the time point at which the notice is to be transmitted.
However, when deceleration using the regenerative braking force of an electric motor is used in such coasting, a torque corresponding to the regenerative braking force acting on coasting, i.e. a coasting torque may generally provide less deceleration, thus entailing the risk of interfering with traffic flow.
Therefore, when applying a function of indicating to the driver information about the coasting time point, a torque different from a general coasting torque may be applied. This will be described below with reference to FIG. 2.
FIG. 2 is a view for explaining the concept of coasting guidance via general coasting-line adjustment.
Referring to FIG. 2, the line, which represents variation in vehicle speed relative to distance when a coasting torque, which is applied to general coasting, is applied, may be referred to as a “basic coasting line”, and the line, which represents variation in vehicle speed relative to distance when a torque greater than a general coasting torque is applied, may be referred to as an “increased coasting line”.
When the increased coasting line is applied to coasting time point guidance, the effect of increasing fuel efficiency suffers somewhat compared to FIG. 1, but a deceleration may be performed at a level that does not disturb the surrounding traffic flow, and thus the coasting distance is reduced to some extent. The increased coasting line is usually set based on the determination of an engineer.
However, even if both the basic coasting line and the increased coasting line are used as described above, since the required coasting distance is uniformly calculated depending on the current speed, the target speed, and the remaining distance, an accelerator pedal release time point may be guided without considering the type of deceleration event or the driver's tendency. In particular, problems based on the driver's tendency will be described below with reference to FIGS. 3 and 4.
FIG. 3 is a view for explaining a problem when general coasting time point guidance is applied to drivers who have a tendency to drive slowly or defensively.
Referring to FIG. 3, when general coasting time point guidance is provided to drivers who have a tendency to drive more gently (slowly or defensively) than an average driver, such drivers are less likely to benefit from coasting guidance. That is, since drivers who have a tendency to drive defensively tend to release an accelerator pedal operation (APS off) in advance before the vehicle reaches a coasting guidance point, the vehicle may apply the basic coasting line, rather than the increased coasting line depending on a coasting guidance function. In this case, the driver cannot receive guidance about a coasting time point and the possibility of hydraulic braking is increased due to an increase in the amount of braking near a target point, which may deteriorate regenerative braking efficiency.
FIG. 4 is a view for explaining a problem when general coasting time point guidance is applied to drivers who have a tendency to drive aggressively.
Referring to FIG. 4, when general coasting time point guidance is provided to drivers who have a tendency to drive more aggressively (offensively) than an average driver, such drivers feel that the guidance time point is early and still tend not to follow the coasting guidance. That is, since the drivers do not participate in coasting guidance because they feel that it is too different from their actual driving habits even at a guidance time point based on the increased coasting line, the effect of the coasting guidance function may not be seen at all.